Centrifugal pump



June 17 1947- L. G. HowE Er AL4 2,422,415

CENTRIFUGAL PUMP v Filed Dec. 15, 1943 3 Sheets-Sheet l f @mii I 2f j f5 54 f NVENTOR5. fw/.s f Kar/E BY fL ME@ 1D. S14/7H and June i7, 1947. L. G. HowE ET A1.

CENTRIFUGAL PUMP Filed Dec. 13,y 1943 3 Sheets-Sheet zal! . ,w 5. d. M R ns., N o WM MWWMM vfm r.

June 1 7, 1947. l L. G. HowE, Er AL 2,422,415

CENTRIFUGAL PUMP Filed Dec. 13, 1943 5 Shee;cs-Sheet 5 Patented June 17, 1947 UNITE-D STATES PATSENT OFFICSE CENTRIFUGAL 'PUMP poration of Indiana Application `December 13, 1943, SerialNo.=f14,034

(Cl. M3-406) Claims.

This invention relates toa centrifugal pump, yand especially to a two-stage 4centrifugal pump in which the two stages may be operated Veither in series or in parallel and which -is `especially adapted to be mounted .Ona vtruck for -fire .iightingfpurposes.

The conditions of use for such a `pump and its suitability for integration with other necessary equipment on -a lire truck impose severe requirements. The pump must be reliable and eiilcient. To this end, `it mustfbe :simple yto operate and to maintain, land hence -must be composed of relatively simple parts arranged in yan accessible manner; and its water passages must fbe either straight or smoothly curved,l and must be arranged to avoid air lock. It must be well adapted for mounting on the truck, and hence must be compact and arranged to use economiically the space it occupies; and it must be re1- .atively light in weight. It should have inlet .and outlet vopenings on both sides of the truck, so that it may be connected from :either side, and must operate efficiently when connected from either or both sides. It must operate elciently either when its stages are 4in parallel or when they are in series, and must be easily converted from one condition of operation to the other.

It is the object of this invention rto provide an improved series-parallel centrifugal pump which will meet these requirements. The vpump embodying this invention is desirably composed .of two. main Castings, ntting .together yin a hori- Zontal plane. The lower .casting is adapted to be mounted transversely on the frame of a truck, and Aforms an intake manifold with intake openings at both ends. Two centrifugal pump units are-formed in the castings, on -a common aXis in the .plane of separation of the two castings, with that common .axis spaced from .the center of the lower casting (to the right `in the drawings) toward one end .of the pump assembly, so that it will lie near one side of .the truck. The volutes for .the two pumps vdischarge at the top of ythe pump units, and long, substantially straight diiusers lead from them with a slight upward inclination toward the opposite end of :the pump assembly. A double-ended outlet manifold, extending parallel with the intake vmanifold lies .between the disch-arge ends vof the dilusers.

Onel of the difiusers is in .open communication with the outlet manifold. The other diluser leads into vthe open end of a cup-shaped valve, may be `turned to `discharge through its side outlet either laterally into the outlet pas-.

`Sager-.for paralleloperanon of; the-pump uaitsef.y

or downwardly .into a .return passage. .That return passage leads=downward1y `from that cupshaped valve and transversely beneath the outlet manifold .and the ilrst diffuser and Adiagonally ,back to the suction chamber ofthe pump `unit supplying the rstdiifuserand :is formedso ythat the top wall of the lower casting :is lits iloor. That suction chamber, half Ain the upper casting andhalf in the vlower casting, has -anupwardly opening check -valve in its iloor, which :closes the `suction 'chamber to the -intake `'passage when water enters it at higher pressure-from the return passage-during series operation.

The accompanyingdrawings illustrate .our in- Vention. In such drawings,V Fig vl -is :a -top :plan with lparts broken away to show y.the diiusers and Vthe outlet Amanifold in section; Fig. 2 is -a top plan-of the lower casting; Fig. 3is a Ibottom plan of the top casting; Fig. '4 is a side elevation, with parts broken away .to show the-intake passage, the return passage, and the suction Chamber 4in section; Fig. 5 is a vertical section through the axis-cf the pump units, on line -5-5 of Fig. 4; Fig. 6 is a vertical .partial-section-on the line 6--6 of Fig, 5, showing details of -the check valve; Fig. 7 is a vertical .section on the line 'I-'I of l; Fig, .8 is an isometric view with the `valve-elfldof the upper casting out away in `theplaneof Fig. '7, and with other parts broken away and shown in section to illustrate series operation of the pump; and Fig. 9 is a vertical partial-section on the line 6 6 of Fig. 5 showing a modified form vof .the -floor of the return .passageatits outlet end.

The pump shown in the drawings ris made of two mai-n castings--a lower .casting i0 andan upper casting II-arranged withhorizontal mating faces in a plane containing the .axis of the main shaft I2 of the pump. The lower casting, best vseen in Figs. 2 and 4, is adapted v.to b e mounted directly on the longitudinal vfratrie members 9 of a truck and .to be secured thereon by mounting pads I3. The lower casting forms an undivided .intake manifold .I4 extending throughout its length and having an intake port I5 at eachend, desirably provided with a mounting flange to receive a tting (not shown) to which intake hose may .be attached. The intake ports I5., only one of which -is shown,v are symrnetrical and equally spaced from the respective mounting pads I3.

The agis oi the shaft I2 is spaced from the mid point of the lower casting ill toward one end of the .pump assembly-to the right in Fig. e. The portion 4of that casting I-.Il adjacent. to

. the shaft I2 is widened and deepened, and is provided with a plane top surface I6 to receive the mating lower surface I1 of the top casting II. As is seen in Figs. 2 and 3, those mating surfaces have a generally rectangular portion, and a narrower diagonal portion I8 leading to a transverse portion I3 near the opposite end of the pump assembly.

At the widened portion of the lower casting, the two castings I and I I are shaped to form the two pump units A and B. The main shaft I2 of two pump units is received with the axis of the shaft lying in the plane of the mating surfaces I6-I1 along the transverse center line of the rectangular portion of those mating surfaces. Reading along the axis of that shaft I2, from the bottom to the top of Fig. 2, from top to bottom in Fig. 3, and from left to right in Fig. 5, the parts formed in the castings are as follows:

First, there is a mounting plate for mounting either the outboard bearing 2I or the driving transmission 22 which embodies outboard bearings for its end of the shaft I2. Next, there is an outer side-wall formed to receive a packing gland 23 for the shaft I2, then a suction chamber 25 for pump unit B.

The .top and one end of the upper half of this suction chamber 25 is formed of a curved wall 25 in the upper casting which extends upwardly from a flange forming part of the mating surface I1. In the lower casting I0, the suction chamber 25 is defined at its ends by walls 24 and 26 and at its bottom by a check valve seat 21.

The wall at the inner side of the suction cha1n ber 25 forms one wall of the impeller housing of pump unit B, and provides a seat to receive a wear-ring 3| t0 surround the eye of the impeller of the pump unit B.

An inner impeller-housing wall lies beyond said first wall, and a volute 32 is formed at their outer edges. Beyond the impeller-housing of pump unit B, thev castings carry a bearing-spacer 34; then form the impeller-housing and volute 35 for pump unit A; then a seat 35 for a wear ring 31, to surround the eye of the impeller of pump unit A; and then a suction chamber 38 for pump unit A.

The upper half of the suction chamber 33 is defined by a semi-cylindrical top wall 39 formed on the upper casting l I. Its lower half, however, is fully open to the intake passage I4, andthe horizontal, planar, top wall IB of the intake passage I4 extends without obstruction on its lower Asurface to an opening in it which defines the suction chamber 38. This freedom from obstruction and pockets on or in the top wall of the intake passage I4 permits any air in the intake manifold I4 to escape freely into the suction chamber 38, from which it will be discharged. Because the intake manifold I4 is undivided, air will also be discharged by this path from adjacent to the depending lower walls of the suction chamber 35 of pump unit B. Pumps of this type are usually car- YA, the outer wall is formed to receive a packing gland 42 to seal around the main shaft I 2. This outer wall carries a mounting plate 43- similar to mounting plate 23, to receive either the driving transmission 22 or the outboard bearing 2|. The use of opposite mounting plates 2Q and 43 similar f spectively. Each of such impellers has an inlet eye 41 which has a running fit with its associated wear-ring 3| or 31, and has suitably designed impeller passages extending toward its periphery to discharge into its associated volute.

The volutes of the two pump units are of grad- Y ually increasing cross-sectional area, beginning at the top, substantially at the plane of line 5 5 in Fig. 4, and proceeding counterclockwise around the pump units to discharge points which also lie substantially at the plane of line 5-5 in Fig. 4. At such discharge points, the volutes merge smoothlyinto diifusers A50 and B55 for the respective pump units A and B, which continue a gradual increase in cross-sectional area, rihe axes of the diffusers are substantially straight, but have a slight divergence between them and a slight rise as they lead to the right in Figs. 1, 4, and 8 toward the opposite end of the pump assembly. By reason of the displacement of the pump-axis toward one end of the pump assembly, and leading the diifusers toward the opposite end,V the diffusers may be both substantially straight and relatively long. In the pump shown, they have a length of .the order of one and one-half times the diameter of the pump impellers and 45. v Y

An outlet` manifold passage 5I'lies between the discharge ends of the two diffusers and extends in both directions to outlet ports 52 presented respectively to opposite ends ofthe pump assembly. Each outlet port 52 is provided with means such as a suitable flange to receive discharge ttings (not shown) which may have any desired number or arrangement of iire hose connections. The outlet passage 5I is of substantially uniform crosssectional area throughout its length, and for this purpose aswell as to decrease weight, its lower wall dips between the two pump units to below the level of the volutes 32 and 35. To facilitate mounting the pump in a truck, and maintenance of it without removal therefrom,the outlet manifold 5I is relatively shorter than the intake manifold I4. A y

The discharge end of diffuser Beis in open communication withthe outlet passage5l. The diffuser A- leads into the open end of a cupshaped valve 55, substantially co-axial with the terminal portion of the diffuser. The valve 55 forms a smoothly curved passage leading to an outlet through its side, and has one position in which that side openingcommunicates with 'a port into the outlet manifold 5I, in which position of the valve 55 two pump units AY and B operate in parallel.

The cup-shaped valve 55 i-s mounted in a cylindrical recess co-axial with the' discharge end of the diffuser A-5D and withV its axis generally Y parallel to the axes of Vthe manifolds I4 and 5I.

The valve-receiving recess is formed in the end of the upper casting II where it may easily be machined. The valve 55 is held in that recess by a plate 51, through which the axial valve stem 58 for the valve 55 extends. This position'of the and outside the outerwall Glicitl'iewtruck'I on whiclrthe pump is 'mounted'.

The valve 55'* has' a: second position, sliownin Fig; 8*, ,in'which its side opening i-sdirecteddown-y ward:` From this position of the valve open-ing, a` return passage-tl` leads downward through a smoothcurve and horizontally beneath the discharge manifold falend-diffuser Bi-5anddiagonally fbaiclrtowar lA and to thesuction chamber 25 forpump.unitn B. The top and'side walls of this return' passagel arey formed-in theupper casting I1; but itsv lowerwall is formed by the toppsurfacel i6 'of the lower casting.

With thevalve 55 in itsy second position, to discharge into the return passage -I; the discharge from pump unit A through diffuser A-E- is. led through'that'returnV passage 5l to the suction chamber 25 of pumpiunit B. Av check valve G2; on the'seatZ-l (seeligs. 2,v 4; 5,- and` 6) in the floor of thesuctionv chamber 25,- then closes thaty suction chamber 25 against communication with the intake manifold ill; and pump unit B is sup: pliedwholly by'waterrfrompump unit A. The two pump units thenY operate in series.

The check valve 62/ is generally rectangular, but has themid-portion-of its free side edgefcut out, to clear the main shaft l when the valve is. in open position and'to clear the lower portion of; the seat-'Stof the wear-ring'ilwhen the valve approaches closed position; and the valve seat 2 is suitably shaped-to conform with this cutout configuration.

Pivot pins 63' and 511 are formed atd the ends of the opposite side of the checkvalve 62'.- In one modification (Figs. 4 andi-5)'tl'ie` pivotl 63' isA re'- ceived'in a socket formed in the'end-'wally 24* of the. suction chamber 25'; and pivot 64 is received in the bottom of avertical slot formed in the end-wall ZB'of the suction chamberI 25: A bolt 55 passing through the outer side wall ofy intake manifold is and across theslot 65 serves tokeep the pivotV B'tinplace. By removal'of'thebolt 56, the valve @Amay be lifted-from itsy seat andremoved. In anothermodication (Fig. 9)', each pivot pin 63, and Sais received in` a slot 65 and held in place by a bolt E5 insertedv from outside through the side wall. of the lower castingy l0'. An accessopening 61, normally closedlby a plate 68, is formed' in theupper curved wall 25 of suction chamber ZEto, permit'access'toV the check*- valve 52'in the event. that it' becomes. fouled lby foreign matter.

The. valve. 62,. incross section, is formed with a slight taper from its pivot'edge toits free edge; and its top surface (when closed) is provided with a series of spaced ribs Se. extending from the pivot side .ofthe valve toward the free edge thereof. When the valve 52 is in open position, these ribs lie against the outer side wall of the'intake passage lli, and provide between them spaces which are'open atthe free edge of the Valve.

When the pumpv is changed from parallel to series operation,l and the discharge from pump unit A is l'ed'through return passage 5l to the suction chamber 25 of'pumpunit B.fiow of'water through the port formedV by the seat 2T of the check'valveV 6l is reversed; and lb'y'theclosing of the valve 6|", is stopped.v During any-such reverse,- orV downward'fiow through suchv port, the spaces rbetween the ribs iii) and behind the valve 52'ware open against thedirectionA of that reverse flow,v andthe water enters those spacesto exert a'positive force ytendingto move thevalve 62 from its-open position.y

In the modification oi- Fig. 6, where the end walllffof" the'lowe-rfpart of the suction chamber 2f5-isvertical, andreverse flo-w of water would' be generally downward at the free edge of the valve 62; in'open'position, the ribs 69 are normal to that top edge.- In the lmodiication of Fig. 9, however, wherethewall 24? of the suction chamber 25 is a downwardly inclined continu-ation of-'thev floor iSof the return passagetfl, and thereverseflow4 of water' would be1 diagonal at the freeedge and one-end-o-fithevalve 6l, the ribs' 69 are desinalbly disposed` diagonally, to present the spaces Iloetween theri'bs 69 more directly against that direction oi'ow.

Paralleloperation ofA thev pumps as follows: The manual' valve 55 isturned to the position shown in Fig. '7, in which waterpassingthrough it willv Ibedischarged into the outletl passage 5i; and the, return passage (iln will beV cut 01T' from communication with t'hevdiffuser A-Et InV this condition,4 each of' the two pump units A and B will'receive-water'from the intake passage` M; by way'ofthe suction chambers 25 and 38, that water will 'be discharged from the volutes 32" andl 35 from ther pumps into the two diffusersA 50; In thosedi'ffuser passages, the; velocity of the water will be reduced', and. its kinetic energy will be substantially changed toA pressurezenergy. From v both diffuser passages 5.9, the water willowinto the` outlet. passage 5l and, will be discharged through whichever one of the. outlet ports 52' is open, as'4 to communicate withv one or. more fire hose.

Parallol'operation of the pump will deliver a relatively large quantity of water, atY the pres- Sule givenito it by the action of a single-stage pumpV unit-a lower pressure thank when the two pump units act in series.

Series operation ofv thepump, best shown in Fig; 8; is as follows: The manual valve 55- is turned to its downwardly open position as shownl in Fig. 8; to discharge into the return passage 6l and" to-cut off communication between diffuser A--'il'and' the outlet manifoldl 5l. In this` con-v dition, waterwill flow from intake `passage Il through the suction chamber 38 to the pumpunit A, and will be discharged through its volute 35 toy/.the diffuser. Ae-ii'f.. In that diffuser A-- the velocity. off thef water. will ibe reduced, and* the kinetic energy imparted to it by pumpl unit A will? be largely. changed' to pressure energy'.Y

.Thewat'erwillthen have thepressure impart edbyiy asinglepumpestage. Then, asshown by` thev arrows in Fig. 8;. it' will ow through the. downwardly/open' portici manual valve 55-into the transfer., passage Stand; will be led'. back to the suction chamber4 2.5 of pumpunit-B; The water. reaching'suetion chamber 25. from there.- turn passage 6i", being at a higher; pressure thantheA waten in the. intake. passage Mr.. willltend tov awpashcheck: valveinto that intake pasm sage.` L4; As hasbeenpointed out,.any such. iiow will; forcerwateri behind', the check-valve E2; to close it;v Once closed; the pressure. differential will hold it in. closed position..

With; valve 621 closed, the waterv` discharged' from diffuser. A -t andifledfto. pressure chamber ZEby the, retumpassage 5i will enter pump unit Bwill beiacted upon thereby',l and; will 'oe discharged from thatfpump with. added energy` intozvolute 3.2,' and tiience'into diiTuser B-5!3.. In the diuser B;-5i; the kinetic; energy added' to the-'water .byupurnpunit Bf' will be largely changed topressu-relenergy, andfthewater willlthen be dischargedifrom diffuser Be-El into the outlet manifold- 5 I;

surface, which facilitates preparation and assembly. The surface of the lower casting is made to serve as the floor of substantially the only passage which would otherwise be difficult to core in the casting procedure, and thus further facilitates manufacture. If necessary, the pump may be disassembled readily and without removal from its mounting on a truck.

The pump may be connected from either or both sides of a truck on which it is mounted. It may be connected to draw water either from a hydrant or from some natural source such as a river. Its two pump units may be operated either in series Vor in parallel, and change from one to the other is accomplished by manual operation of but a single handle, conveniently located. The valve so operated is placed for easy connection to its handle and its simple construction facilitates its assembly and minimizes maintenance requirements. The single check valve of the pump is reliable in operation and is easily accessible without dismantling the pump in the event of its being fouled by foreign matter in the water.

The water passages of the pump, while compactly arranged, are straight or smoothly curved, particularly those passing water at highvelocity, Long, substantially straight diifusers merge smoothly from the pump volutes, to give good transformation from the kinetic energy imparted to the water by the impellers to pressure energy delivered at the outlet manifold. The construction makes for ease of manufacture, adapt` able`mounting, simplicity of operation. and efficient pumping.

We claim as our invention:

1. In a series-parallel centrifugal pump adapt'- ed to be mounted transversely on the longitudinal frame members of a truck and comprising an upper and a lower housing mating in a horizontal plane, the lower housing forming an intake mani.

fold with opposite end-inlet ports, and an outlet manifold inV said upper housing with opposite end-outlet ports presented parallel with said in.. take ports, the combination of a pair of pump units formed in said housings, a main shaft for said pump units on a transverse axis in said mating plane, impellers in said pump units and mounted on said main shaft, said axis and pump units being offset toward one end of said intake manifold, volutes for said two pump units terminating adjacent to a vertiical plane containing the axis of the pump shaft, diifusers of gradually increasing cross-sectional area merging from'said volutes substantially tangentially and leading toward the opposite end of the outlet manifold, one of said diffusers being in open communication with said outlet manifold, a valve recess at the end of said other diffuser, an outlet port from said recess to said outlet manifold, a suction chamberfor the pump unit supplying said open diffuser, a return passage leading from said valve recess downwardly and transversely between the outlet and intake-manifolds and back to said suction chamber, an intake port in the floor of said suction chamber for inflow from said intake manifold, a check valve to prevent reverse ow through said intake port, and a manually operable valve in said valve recess to receive the discharge from said other diffuser, said valve having a position in which it discharges into said outlet-port and a second position in which it discharges into said return passage.

2. The combination set forth in claim ,1, in which said valve is a cup-shaped valve co-axal with the discharge end of its associated diffuser and is arranged to receive water through its open end and to discharge such water throughV a side opening, the axis of said valve being substantially parallel with the axes of said intakeand outletmanifolds. Y I

3. In a series-parallel centrifugal pump, a rotor, a spaced pair of impellers mounted on'said rotor, volutes for said impellers, an intake passage below the common axis of said impellers,

said two volutes being arranged with their disj charge ends at the top, a diffuser of gradually increasing cross-sectional area leading tangen- Atially from the discharge end of each said volute, j

the axes of said `diffusers being Substantially straight and co-planar, an outlet passageY extending in the same direction as said diffusers and passing between them, the end of one of said diffusers being in open communication with said outlet passage, a return passage leading from the discharge end of the other of said diffusers downwardly and transversely beneath said outlet passage and said one diffuser above the level of the,

axis of said impellers to open communication with the inlet side of the rotor supplying said one diffuser, a check valve between said impeller inlet and said intake passage, and valve means at the end of said other diffuser to direct the outow therefrom either to said outlet passage or'to saidV return passage.

4. In a series-parallel centrifugal pump, a'pairV of co-axial pump units formed in apairl of main castings separable on a horizontal plane containing the aixs of said pump units, diffusers leading from the tops of said units generally in the same direction and substantially horizontally, valve means at the end of one of said diffusers to direct the discharge thereof into confluence with the discharge from said other diffuser, and a return passage leading downwardly from said valve means, curving to horizontal and rearwardly below said other diffuser and abovethe level of said pump axis, a suction chamber at the inlet of pump unit .associated with the other of said diffusers, said return passage Vbeing Vconnected to said suction Ychamber and having its top and side walls formed in the top main casting and its bottom wall on the Vbottom main casting.

5. In a series-parallel Vcentrifugal pump, a pair of co-axial pump unitsdiifusers leading from the tops of said units generally in the same direction and substantially horizontally, valve means at the end of one of said diffusers to direct the discharge thereof into confluence with the discharge from said other diffuser, and a return passage leading downwardly from said valve means, curving to horizontal and rearwardly below said other diffuser and above the level of said pump axis, a suction chamber at the inlet of the pump unit associated with the other of said diifusers, said return passage being connected to said suction chamber, a check valve in said suction chamber pivoted on a generally horizontal axis below the inlet to said suction chamber from saidV return passage, said valve having an upright open position against a side-wall of said suction chamber, channels in the back face of said valve open at a free edge thereof and positioned to form with said wall pockets which are open against the direction of ilow from said return passage to the port for said check-valve.

6. In a series-parallel centrifugal pump, a housing forming an intake manifold, a pair of pump units with their lower halves formed in said housing, the impellers of said two pump units being mounted on a common shaft the axis of which lies in the upper Wall of said housing, a suction chamber for one of said pump units, the lower portion of said suction chamber being formed between the casing of its associated pump unit and the outer wall of said manifold housing and by transverse walls depending from the upper wall of said manifold housing, a valve seat formed at the lower ends of said depending walls, a check valve pivotally mounted adjacent the outer housing wall and operable to prevent flow from said suction chamber to said manifold, a discharge passage to which the pump unit associated with said valved suction chamber is connected, means including a valve for directing the discharge from said other pump unit either to said discharge passage or to said valved suction chamber above the valve therein,

7. In a series-parallel centrifugal pump as dened in claim 6, said check Valve pivotal mounting comprising a pivot pin and socket at one end, a pivot pin carried by the other end of said check Valve, a vertical slot in the depending wall at said other check-valve end to receive said pivot pin at its bottom and permit said pivot pin to be lifted, and a bolt insertable from outside said pump to lie across said vertical slot to hold said pivot pin in pivoting position.

8. In a centrifugal pump, an intake manifold having a horizontal top Wall, a pair of pump units formed with their axes lying transversely across said top wall, a suction chamber for one of said pump units with its lower half dened by Walls depending from said top wall and communicating with said manifold therebelow, a suction chamber for the other pump unit in open communication with said intake manifold at said top wall, said manifold being formed to permit free ow from adjacent said depending Walls to said open communication.

9. In a series-parallel centrifugal pump, a discharge passage, a pump unit on an axis transverse to said discharge passage and spaced rear- 10 Wardly from an outlet of said discharge passage, a substantially straight diffuser extending from said pump unit to a terminal portion generally parallel with said discharge passage at its said outlet end, a cylindrical valve casing co-axial with said terminal portion at the discharge end thereof, a cup-shaped Valve in said valve casing having an open end positioned to receive the discharge from said terminal portion, a side discharge opening in said valve, a valve operating member extending axially from said Valve in the same general direction as said discharge passage outlet, a second pump unit, passages leading from said valve casing respectively to the inlet of said second pump unit and to said discharge passage, said valve having positions to discharge respectively into said passages from said valve casing, and a valve associated with the inlet of said second pump unit to close its normal supply passage when said first pump unit discharges to said second pump unit.

10. In a series-parallel centrifugal pump, a pump unit, a generally straight diffuser passage leading from said pump unit, a cylindrical valve casing at the end of said diiuser substantially co-axial with a terminal portion of said diffuser, a cup-shaped valve in said casing having an end inlet opening forming a substantial continuation of said diffuser, a side discharge opening in said valve, two circumferentially spaced ports in said cylindrical valve casing, a second pump unit, a discharge passage connected to receive discharge from said second pump unit, means connecting said ports respectively with said discharge passage and with the inlet of said second pump unit, and a valve associated with the inlet of said second pump unit to close its normal supply passage when said rst pump unit discharges to said second pump unit.

LEWIS G. HOWE. ELMER P. SMITH. RUSSELL K. ANNIS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS FOX Apr. 21, 1936 

